The present invention pertains to a controllable shock absorber comprising a damping cylinder filled with damping fluid, with a piston rod linked with a damping piston sliding therein, said piston dividing the damping cylinder into two working spaces, and with at least one controllable damping valve that permits control of the damping force in the push and pull stages.
The design of a controllable shock absorber is disclosed in EP 0 651 174 A1, in which an additional and controllable damping valve systemxe2x80x94designed here as an additional valve assembly adjacent to the shock absorberxe2x80x94is located between an operating space and a pressure reservoir of a level-control system, and optionally also within a bypass between the two working spaces of a shock absorber, but where the latter is only mentioned and is not further discussed.
With the assistance of the controllable damping valve system presented therein, it is possible, of course, to adjust in the push and in the pull stage four different characteristic curves of the damping force, so that ultimately it is possible only to set a more or less specific xe2x80x9cfirmnessxe2x80x9d of the damping of the shock absorber, which is then the same for the entire operating range, or for all stroke or damping variations at this setting.
For modern motor vehicles with electronic chassis control, such as those with an electronic stability program (ESP), anti-lock braking system (ABS) or anti-slip regulation (ASR), operating individually or in combination, the setting of a specific characteristic curve with a more or less firm damping is only conditionally helpful, since for a fast electronic chassis control that will respond in fractions of a second to hazard situations, a variable damping control adapted to these situations cannot be effected by means of specific and preset characteristic curves.
Therefore, it was an object of the present invention to have a damping control, suitable for incorporation into electronic chassis controllers, which will permit adjusting the damping force within extremely short control times, and in addition, one that will not just follow specified defaults/characteristic curves, but rather one that can be adapted to the framework of ancillary control systems relevant to the chassis, and that can be incorporated into a comprehensive algorithm and a system of electronic chassis control.
The above and other objects can be achieved by a controllable shock absorber comprising a damping cylinder filled with damping fluid, with a piston rod linked with a damping piston sliding therein, said piston dividing the damping cylinder into two working spaces, and with at least one controllable damping valve that permits a control of the damping force in the push and pull stages, such that the controllable damping valve is located within a passage that is located between the lower working space found beneath the damping piston, and the upper working space located above the damping piston, and in which the controllable damping valve is designed such that during a piston stroke in the push or pull stage, a flow through the passage that is variable over the duration of the piston stroke can be controlled by means of a variation in the flow cross section at a minimum of one point of the passage.
In this regard, the controllable damping valve is located within a passage that is located between the lower working space found beneath the damping piston, and the upper working space located above the damping piston. The controllable damping valve is designed such that during a piston stroke in the push or pull stage, a flow through the passage that is variable over the duration of the piston stroke can be effected by means of a variation in the flow cross section at a minimum of one point of the passage.
An alternative design solution that is still consistent with the invention of a controllable shock absorber comprising a damping cylinder filled with damping fluid, with a damping piston sliding therein, such that said damping piston is linked with a piston rod and equipped with pressure-dependent valves for the push and pull stages, and where said damping piston divides the damping cylinder into two working spaces, and which is equipped with an additional control valve/controllable damping valve that permits control of the damping force in conjunction with the pressure-dependent valves at the damping pistons of the shock absorber in the push and pull stages. It is a feature according to this invention that the control valve is located within a bypass that is located between the lower working space found beneath the damping piston and the upper working space located above the damping piston, wherein the control valve is designed so that during one piston stroke in the push or pull stage, a flow through the bypass that is variable over the duration of the piston stroke can be controlled by means of a variation in the flow cross section at a minimum of one point of the bypass.
Due to the presently invented design of a controllable damping valve/control valve, it is possible to achieve very short control times and to integrate control of the damping force of the damping into the other electronic chassis controls. Thus, for example, during emergency braking of a motor vehicle, the pitching motion caused by the shift in axle load, i.e., the pitching motion originating from the increased load on the front wheels and the associated, increased jounce of the front axle can be influenced by an ever diminishing flowxe2x80x94specially in the initial phasexe2x80x94through the bypass for the duration of the stroke of the damping piston in the push stage and by the increasingly firmer shock damping associated with it during the piston stroke. In addition, a corresponding, simultaneously increasing, softer damping control can occur at the rear axle.
In a similar manner the rolling movement occurring due to a shift in wheel load during sudden steering and evasive maneuvers can be affected by means of appropriately different damping control for the curve-interior and curve-exterior wheels. The same also applies to yawing motion, i.e., during motions of the vehicle about its vertical axis. If all this is done in the framework of a combination, e.g., with controlled braking of individual wheels in an electronic chassis control, then a significant improvement in driving stability will be achieved from this kind of damping control, in particular in extreme driving situations.